The wireless sensor network is a new technology, and the network is formed by a large number of low-cost mini-sensor devices arranged in a monitoring area. Generally, the sensor devices have a simple structure, low energy consumption, and low cost, so the reliability thereof cannot be ensured.
However, in actual applications, some requirements for Quality of Service (QoS) indexes including the reliability must be met in some cases, for example, the control application of an industrial environment, and the issuance and notification of some important information. Accordingly, some technologies for solving the QoS problems such as the reliability are proposed.
The most direct method for improving the reliability of data transmission is to retransmit messages to ensure the reliability of the data sending. For example, if a sending device does not receive a response, it sends the message again, till a response is received or maximum sending times are reached. Although the method is simple, the ensurance for reliability is not enough. In addition, the inventors found that this solution at least has the following problems. The retransmission is equivalent to time diversity and does not have obvious effect for resisting long-term interference, that is, the retransmission mechanism cannot resist the long-term interference suffered by the device. Furthermore, the retransmission increases the delay of information transmission, while reliability and low delay are both required for some critical data, so the retransmission is not always suitable. Additionally, the retransmission also consumes more energy.
To ensure the reliability of the data sending, when the distance between devices remains unchanged, the signal transmission power of a transmitter can be increased. For example, a signal amplification circuit is added at the signal transmitter, and the original output signal is amplified and then transmitted. This solution is simple and easy to implement, and is applicable in many scenarios. However, the inventors found that this solution at least has the following problems. Higher signal transmission power will result in more energy consumption, thus for the wireless sensor devices with a battery as the energy source, more battery energy is consumed if the transmission power is increased, the life of the device is reduced, and the operation cost of the network is increased. Moreover, as the signal is transmitted omnidirectionally, and the increased signal received by the receiver is but a small part of the increased transmission power due to the limit on the receiving range, the increase of the transmission power does not have obvious effect on the receiving effect of the receiver. Further, the increase of the transmission power of a single device will increase the interference on devices nearby, thus the background noise of other devices is increased, and the reliability of data transmission of other devices is lowered.